1. The lightweight, elastic outer bark of the cork oak, used especially for bottle closures, insulation, floats, and crafts.
2. a. Something made of cork, especially a bottle stopper. b. A bottle stopper made of other material, such as plastic.
3. A small float used on a fishing line or net to buoy up the line or net or to indicate when a fish bites.
4. Botany. A nonliving, water-resistant protective tissue that is formed on the outside of the cork cambium in the woody stems and roots of many seed plants. In this sense, also called phellem.